Accurate control system for axial load bulge forming



Aug. 15, 1967 K. E. EARLY 3,335,590 ACCURATE CONTROL SYSTEM FOR AXIALLOAD BULJGE FORMING 2 Sheets-Sheet 1 Filed Aug. 7, 1964 SEEN l .1 J mINVENTOR. Kf/Y/YET/l E. 54152) Aug. 15, 1967 WATER V SUPPD V REL REL 50$01. 56 T I,

CAM T $1 4.

K. E. EARLY ACCURATE CONTROL SYSTEM FOR AXIAL LOAD BULGE FORMING FiledAug. 7, 1964 2 Sheets-Sheet 2 Ly ELECTRICAL VALVE SOURCE 70 SOL I -34 42I 74 OIL sum) 44 United States Patent 3,335,590 ACCURATE CONTROL SYSTEMFOR AXIAL LOAD BULGE FORMING Kenneth E. Early, Seattle, Wasl1., assignorto The Boeing Company, Seattle, Wasln, a corporation of Delaware FiledAug. 7, 1964, Ser. No. 388,201 3 Claims. (Cl. 72-58) ABSTRACT OF THEDISCLOSURE The invention is directed to axial load bulge formingapparatus which is controlled by a system comprising (i) a segmentedsplit die, (ii) a compression system to close .This invention relates toaxial load bulge forming apparatus, but more particularly to a controlsystem for programming the forming sequence of tube blanks into complexshaped parts, having various diameters and radii along its length, byliquid volume control.

In the prior art the forming of tube blanks into complex shaped partshaving a variety of diameters and radii was based on a system that waspressure oriented. In order to form a part the pressure necessary toform the part into its desired shape was calculated and a certain amountof pressure was' determined. However, because of the variation in wallthickness of a tube blank and the difference in temperate strength alongthe length of the tube blank the parts thus formed in accordance to thissystem were all different and needed very often additional and specialtreatments. For example: some parts needed .tobe anodized and others hada larger or,smaller diameter and thus had to be rejected. It wastherefore obvious that each tube blank could not be treated with thesame pressure as was calculated and that for each tube blank a differentpressure was needed in order to form equal shaped-parts. Thus theinadequacy was traced to minute variations in gage thickness, heat treatconditions and tube geometry which are unavoidable under normalproduction conditions. Another technique used in the, prior art forforming of tubes and tube fittings, which involved small radius bendsand a large degree of diametrical expansion, comprised the use ofinternal rubber pressure to bulge form the part to the dieconfiguration. A second used a rigid die arrangement and both techniquesrequired the .use of extremely high forming pressures. Also suchinternal pressures tend to lock partially formed sections of the tube tothe dies flat surfaces. This means, in the case of the first technique(simple bulge forming), that the material must be stretched bothcircumferentially and axially to form to the die configuration. Suchstretching, together with the high pressure exerted, resulted in a veryhigh incidence of part fracture. In the second case the combination ofbulge forming and end loads, the end load pushed the material intothedie cavity, but the internal pressure forced the material against thedie sun I faces. This often resulted in severe galling of the material,which is a basis for rejection of the finished part. With either ofthese techniques a rejection rate of up to 60% has. been experienced.

In short, the prior art maintains a forming procedure which depends onpressure oriented systems which were 3,335,590 Patented Aug. 15, 1967found to be unreliable for producing parts of a similar shape andvolume. The shortcomings of pressure control are even more evident whenforming long non-symmetrical parts. For example, one of the formulasused to calculate the pressure required to yield (bulge) a tube is shownbelow:

S=yield strength of the tube material in p.s.i. W=tube wall thickness.

R==inside radius of the tube.

P=bulge pressure in p.s.i.

tubular parts by axial load bulge forming apparatus having an automaticregulated forming sequence.

It is still another object of the present invention to form parts by anaxial load bulge forming apparatus having a volume control circuit whichmakes it possible to finish form a tube blank in one operation duringwhich varia tion in tube condition and geometry are automaticallycompensated for.

Furthermore, this invention provides other objects, features, andadvantages which will become fully apparent from the following detaileddescription taken in conjunction with the accompanying drawings whichillustrate and clarify the preferred embodiment of this apparatus, inwhich:

FIGURE 1, illustrates a cross section of a segmented d ie having a tubeblank positioned therein.

FIGURE 2, illustrates the same segmented die as shown in FIGURE 1 withthe exception that the tube blank has been partly deformed by theinternal bulging pressure and the die parts have moved closer togetherby a hydraulic force thus providing an axial load on the tube blank.

FIGURE 3, illustrates the final axial load bulging operationaccomplished in the die and the finished part enclosed therein.

FIGURE 4, shows a schematic diagram of the control system for actualload bulge forming including the die, hydraulic pressure means, liquidsupply pressure means with liquid volume control and an electricalbalancing and switching means.

controlled by a system comprising (a) a split die having segments, (b) acompression system to close to die thus creating axial load on the partin the die, (c) a liquid .volume control system to bulge the part in thesegmented split die and (d) a balance system to coordinate and regulatethe axial load pressure and liquid volume bulging pressure with oneanother.

Referring now to the drawings wherein like reference charactersdesignate corresponding parts throughout FIG- .URES. 1 through 5, thereis shown in FIGURE 1, a split die 2, comprising. several segments 4, 6,and 8, positioned between its stationary top section 10 and its movablebottom section 12, in an extended relationship with one another and witha work piece or tube blank 14 positioned therein. The end portions ofthe tube blank 14 are resting against the movable bottom section 12 andthe stationary top section and it is assumed that this enclosed positionof the tube blank 14 and the top and bottom sections 10 and 12 should bewithin :.010 inch, which would be the particular position of startingthe axial load bulge forming. A pressure line 16 is connected in aliquid tight relationship with the movable bottom section 12 forsupplying liquid into the tube blank 14. A bleed line 18 is connected ina fluid tight relationship to the stationary top section 10 of the bleedoff air.

In FIGURE 2, the split die 2 has changed its shape, the movable bottomsection 12 has moved upwards and thus has compressed the tube blank 14while at the same time the liquid which was fed through pressure line 16into the tube blank 14, has bulged the tube blank 14 into a shape whichstarts to conform to the desired inside configuration of the segments 4,6, and 8. The segments 4, 6, and 8 have accordingly moved and positionedthemselves by the bulging action of tube blank 14 into its correctposition.

FIGURE 3, shows the final stage of the axial load bulge forming andsegments 4, 6, and 8 of the split die 2 which are disposed between themovable section 12 and the stationary top section 10, and the tube blank14 has been formed into the shape and length of the complex shaped partas was required. The closing of the die 2, including segments 4, 6, and8, the top section 10, the movable bottom section 12 and the amount ofliquid fed into the tube blank 14 is regulated and controlled by anaccurate control system.

In FIGURE 4, a schematic diagram illustrates the accurate control systemfor axial load bulge forming wherein volume control of the liquid forfilling of the tube blank 14 and the closure of the die 2 arecoordinated in an automatic controlled sequence. In general, hydraulicmeans 30 are shown to be connected to the split die 2 for creating anaxial load against the tube blank 14. A liquid supply means 32 isconnected to the bottom section 12 of the die 2 for filling up the tubeblank 14 with liquid, also a volume control means 36 is shown to beconnected to the liquid supply means 32 for controlling the amount ofliquid that should be used for bulging the tube blank 14 into itsdesired shape. A balancing means 34 which coordinates and controls theenergization of the hydraulic means 30 versus the liquid supply means 32is shown to be connected with the hydraulic means 30.

The hydraulic means 30 comprises an oil supply 40, a pressure pump 42and a hydraulic cylinder 44, which are interconnected through an oilfeeding tube 46'.

A hydraulic piston 48 is slidably positioned in the hydraulic cylinder44 and provides axial load to the die 2. Energizing of the oil pump 42is controlled by the balance means 34.

The liquid supply means 32 comprises a liquid supply connected to asolenoid valve 50 which is connected through pressure lines 52 with avolume control cylinder 54 and a bulge pump 56. The bulge pump 56 isfurther connected with the movable bottom section 12 of the split die 2by the pressure line 16. The operation of the liquid supply means 32 iscontrolled by the balancing means 34 during the initial startingposition until a predetermined internal pressure inside of the tubeblank 14, and an external hydraulic pressure for maintaining thecritical initial position is established.

The split die 2 is mounted with its stationary top section 10 to theframe member 70. A platform 72 is slidably arranged by guiding means 74between the frame members 70 and 70'. A solenoid valve 76 is connectedbetween the bleed line 18 and the air outlet 78.

The balancing means 34 comprises a limit switch 80, having sensing means80 riding on a cam 82 which is mounted on the movable platform 72, andthus the limit switch 80 is operated by the movement of the platform 72.Furthermore, the limit switch has an electrical circuit connection 84with oil pump 42 and bulge pump 56 in order to energize or de-energizethem depending on the position of the sensing means 86' of the limitswitch 80.

A pressure sensing device 86 is connected to pressure line 16 andelectrically connected to the balance means 34, and this pressuresensing device 86 is adapted to cancel out the efiect of the balancingmeans 34 when the predetermined pressure and critical position isreached. The liquid supply means 32 is provided with a volume controlcylinder 54 which has a piston 90 slida'bly arranged therein and whichpiston has a micro-switch 92 with a sensing member 94 connected thereto.A precisely calculated profile plate 96 is mounted on the platform 72. Amovement of the profile plate 96 will switch on the micro-switch 92 thusenergizing the bulge pump 56, which is electrically connected thereto bycircuit means 88, the bulge pump 56 will then pump liquid from thevacuum control cylinder 54 to the tube blank 14, however, as soon asliquid is pumped out of the vacuum control cylinder 54, the piston 90will move through suction towards the B position which results" in aloss of contact between the sensing member 94 of the micro-switch 92 andthe cam 96. As soon as the contact is broken between the sensing member94 and the cam 96, the micro-switch 92 will stop the operation of thepump 56 until the profile plate 96 has been moved sufliciently upwardsto contact sensing member 94 and the above mentioned operation isrepeated again.

A main switch 100 is connected between an electrical source and balancemeans 34, for supplying electrical current to the balancing limit switch80.

Having thus described and identified the several parts by characterreferences, the operation is as follows:

Operation A tube blank 14 is placed inside of the split die 2 and themain switch 100 is pushed into its on position which energizes the limitswitch 80 and in turn connects the oil pump 42 to the electrical sourceand thus operates the oil pump 42, the oil pump 42 pumps the oil fromthe oil supply 40, through the oil feeding tube 46 to the hydrauliccylinder 44. The piston 48 thus moves upwards thereby pushing platform72 and accordingly enclosing the tube blank 14 between the stationarytop section 10 and the movable bottom section 12 of the die 2. As soonas the critical position which is approximately 10.01 inch, as mentionedbefore, is sensed by the sensing means 80' the limit switch 80 will shutoff the pump 42 through the electrical circuit means 84 and open thesolenoid valve 50 automatically. 7

It will be obvious that any manual operation for closing the tube blank14 in between the top section 10 and the bottom section 12 of the die 2is very difficult, especially in regard to tube blanks which are of avery thin and fragile material because deflection of the material by anover pressure would not be noticed and thus harm the material.

The opened valve 50 will fill up the tube blank 14; and simultaneouslyfill up the volume control cylinder 54 and move the piston 90 from the Bposition to the A position. When the tube blank 14 is filled up with theliquid, the air moves out through the bleed line 18 and its valve 76.The valve 76 will automatically close when all the air is moved out ofthe system and then will electrically actuate the solenoid valve 50 toclose and this valve 50 will then remain closed during the whole forming operation. All the air is now taken out of the system and the volumecontrol cylinder 54 is filled up with a sufiicient amount of liquid forbulging the part into the right shape by volume control.

The sensing means 80' will now sense which of the two pumps 56 or 42should be energized. If the platform 72 is in its critical position thepump 56 will be energized first, if the platform 72 is out of thecritical position, caused by the pressure of liquid in the tube blank14, the pump 42 will be energized first.

Assuming that the bulge pump 56 is energized first, then a pressure iscreated inside of the tube blank 14 which tends to move the bottomsection 12 into a down Ward position thereby moving the platform 72likewise. The sensing member 8i) will sense immediately a downwardmovement of the platform 72 through the cam shaped member 82 and limitswitch 80 will as a result thereof stop the bulge pump 56 and energizethe oil pump 42 and thus increase axial load through the hydrauliccylinder 44, moving the tube blank 14 into its prior critical enclosedposition, which then will be sensed again by the sensing member 80" ofthe limit switch 80. This procedure of alternate operation of both theoil pump 42 and the bulge pump 56 will continue until the aforementionedcritical position (controlled by the balance means 34) and predeterminedpressure (controlled by the pressure sensing device 86) is reached. Thisassures that the forming cycle of each part will start at the sameinitial condition of critical position and internal tube blank 14pressure. As has been stated before, when the predetermined pressure isreached, the balance means 34 is then electrically switched inoperative,(by valve 36 through circuit means 84) thus for the further procedure,sensing means 80 is to be disregarded. Since the conditions of pressureand critical position are now satisfied, the bulging operation canbegin.

The pump 42 is now continuously energized by circuit means 104 to createa continuous axial load, thus closing the die 2. As platform 72 movesupwards profile plate 96 will contact the sensing member 94 ofmicroswitch 92 resulting in energizing the pump 56. A movement of theprofile plate 96 will switch on the microswitch 92 thus energizing thebulge pump 56, which is electrically connected thereto by circuit means88, the bulge pump 56 will then pump liquid from the vacuum controlcylinder 5'4 to the tube blank 14, however, as soon as liquid is pumpedout of the vacuum control cylinder 54, the piston 90 will move throughsuction towards the B position which results in a loss of contactbetween the sensing member 94 of the micro-switch 92 and the cam 96. Assoon as the contact is broken between the sensing member 94 and the cam96, the microswitch 92 will stop the operation of the pump 56 until theprofile plate 96 has been moved sufficiently upwards to contact sensingmember 94 and the above mentioned operation is repeated again. Theamount of liquid which is moved step by step from the volume controlcylinder 54 into the tube bank 14 is carefully controlled by the shapeof the profile plate 96 and thus the bulging volume is regulated incoordination with the upwards movement of platform 72. At a certainstage the sensing member 94 will reach the end of the profile plate 96and this will assure that the proper amount of liquid, as was calculatedfor bulging, has been used. At that moment the pump 56 will be switchedoff by the limit switch 92. The pump 42 (which was switched on when thebalance means 34 was switched off and the bulging operation started)will continue to operate until the die is completely closed and theforming process has been accomplished. However, if during this closingprocess of the die 2 the internal pressure in the tube blank 14 wouldexceed a predetermined pressure, then in order to prevent over bulgingof the tube blank 14 between the segments 4, 6, and 8 a pressure reliefvalve 102 will bleed off this excess. Because the part is in its finalformed shape and practically confined by the die 2, the pressuresensitivity of the part is at this moment negligible. Automatically ormanually the hydraulic pressure will be released and the die 2 opened byits split arrangements (not shown) allowing the part which is shapedinto the desired con-= figuration to be removed.

It will be obvious that the present disclosed manner of axial load bulgeforming by volume control and its automatic system incorporatedtherewith will save a considerable amount of time and also produce amore efficient way of forming.

Accordingly, various minor structural modifications might be suggestedto the preferred embodiment herein described, by way of illustratedexample only it should be understood that many changes could be elfectedto exemplarly structure herein described without departing from thespirit of the present invention, and accordingly, it should be furtherunderstood that the inventor wished to enclose within the scope of thepatent warranted hereon all such modifications as reasonably andproperly come within the scope of the inventors contribution to the art.

I claim:

1. Apparatus for forming parts of tube blanks comprising in combination:

(a) die means having segmented parts slidably mounted in longitudinalrelationship and end portions having support means for holding the tubeblank,

(b) compression means mounted on said die means for compressing axiallythe tube blank thereby adapted to close the segmented die means,

(c) liquid volume control means hydraulically connected with one of saidend portions of said die means for adding a predetermined quantity ofliquid inside of the tube blank,

(d) balance control means for determining the required external axialcompression of the tube blank and said balance control means connectedwith said compression means for sensing movement of said compressionmeans, and

(e) pressure sensing means connected with said balance control means andhydraulically connected with the tube blank for sensing inside pressurethereof and adapted to inactivate said balance control means when apredetermined amount of pressure is reached in coordination with apredetermined axial compression sensed by said balance control means.

2. Apparatus for forming parts from tube blanks as claimed in claim 1,wherein said pressure sensing means is electrically connected with saidbalance means and adapted to inactivate electrically said balancecontrol means when a predetermined pressure is reached in coordinationwith a predetermined axial compression sensed by said balance controlmeans.

3. Apparatus for forming parts from tube blanks as claimed in claim 1,wherein said liquid volume control means is provided with automaticswitching means which Will be activated when the required external axialcompression of the tube blank and the required inside pressure of thetube blank has been reached, said automatic switching means therebyautomatically feeding liquid from said liquid volume control means intothe tube blank in controlled quantities while said compression means isin operation closing said segmented die means.

References Cited UNITED STATES PATENTS 506,247 10/ 1893 Moorfield 72-58788,119 4/1905 Pope 72-58 1,886,831 11/1932 Murray 72-58 2,699,595 1/ 5Zallea 29-421 3,072,085 l/ 1963 Landis 72----62 3,220,235 11/ 196-5Peccerill 72-62 RICHARD J. HERBST, Primary Examiner.

1. APPARATUS FOR FORMING PARTS OF TUBE BLANKS COMPRISING IN COMBINATION:(A) DIE MEANS HAVING SEGMENTED PARTS SLIDABLY MOUNTED IN LONGITUDINALRELATIONSHIP AND END PORTIONS HAVING SUPPORT MEANS FOR HOLDING THE TUBEBLANK, (B) COMPRESSION MEANS MOUNTED ON SAID DIE MEANS FOR COMPRESSINGAXIALLY THE TUBE BLANK THEREBY ADAPTED TO CLOSE THE SEGMENTED DIE MEANS,(C) LIQUID VOLUME CONTROL MEANS HYDRAULICALLY CONNECTED WITH ONE OF SAIDEND PORTIONS OF SAID DIE MEANS FOR ADDING A PREDETERMINED QUANTITY OFLIQUID INSIDE OF THE TUBE BLANK, (D) BALANCE CONTROL MEANS FORDETERMINING THE REQUIRED EXTERNAL AXIAL COMPRESSION OF THE TUBE BLANKAND SAID BALANCE CONTROL MEANS CONNECTED WITH SAID COMPRESSION MEANS FORSENSING MOVEMENT OF SAID COMPRESSION MEANS, AND (E) PRESSURE SENSINGMEANS CONNECTED WITH SAID BALANCE CONTROL MEANS AND HYDRAULICALLYCONNECTED WITH THE TUBE BLANK FOR SENSING INSIDE PRESSURE THEREOF ANDADAPTED TO INACTIVATED SAID BALANCE CONTROL MEANS WHEN A PREDETERMINEDAMOUNT OF PRESSURE IS REACHED IN COORDINATION WITH A PREDETERMINED AXIALCOMPRESSION SENSED BY SAID BALANCE CONTROL MEANS.